DE102007010768B4 - Method for optimizing valve position and pump speed in a valve system with PID control without the use of external signals - Google Patents

Abstract

The present invention provides an algorithm that works with flow reference data that mathematically determines depending on various pump and motor parameters such as speed, torque or power or from calibrated flow curves stored in an evaluation device or from an external flow reference unit such as a flow meter can be. As soon as the valve with PID control has reached its static state, a calculated flow value is recorded and compared with the current flow value, which is obtained after the frequency (speed) of the frequency converter drive has decreased. The valve position is optimized shortly before the speed threshold, at which the flow condition of the algorithm is no longer true.

Description

The present invention relates to a pump including a centrifugal pump, more particularly to a method and apparatus for optimizing valve position and pump speed in a PID controlled valve system without the use of external signals.

The WO 2005/064167 A1 discloses a method in which a calibrated curve is used for power / differential pressure versus flow versus speed. The calibrated data is stored and compared with current values to determine the pump flow. However, while this method can monitor pump performance and differential pressure data to predict flow due to a calibrated pump curve at various speeds, it can not seek optimum pump speed and valve position from a PID control valve system.

The US Pat. No. 6,591,697 discloses a method that explains the relationship of torque and speed to pump flow rate and the ability to regulate pump flow with a frequency converter drive (VFD) to adjust the centrifugal pump speed. While this method can be used to monitor the relationship of torque and speed to pump flow rate and to regulate pump flow using a VFD to adjust the centrifugal pump speed, it can not seek optimal pump speed and valve position from a PID controlled valve system ,

The US 6,464,464 B2 discloses a method that explains a control and pump protection algorithm that uses a VFD to regulate the flow, pressure, or speed of a centrifugal pump. While this method can regulate the flow or pressure through a PID loop embedded in a frequency converter drive (VFD) through feedback signals from an external transmitter, it can not seek optimum speed and control valve position from a PID control valve system.

In the DE 42 43 118 A1 A method of keeping the pressure constant in a multi-point-of-use hydraulic system is described in which a plurality of state quantities are measured which are applied as inputs to a controller, such as a PID controller. In addition to the measurement of current flow values, this method is based on the measurement of pressures in the lines, which lead to the consumption points of the hydraulic system. The controller calculates the adjusted speed of the pump on the basis of these measured state variables based on a sub-control loop and the characteristic diagram of the pump.

In the broadest sense, the present invention has a method and apparatus for determining flow reference data in response to various pump and motor parameters, such as speed, torque or power, or from calibrated flow curves stored in an analyzer or from an external flow reference unit, such as a flow meter , and for using the flow reference data to control a centrifugal pump, a radial fan, a centrifugal mixer or a centrifugal compressor in a PID control valve system. The device may be implemented as a regulator or other suitable processing device for controlling the operation of the pump.

The present invention thus overcomes shortcomings of the prior art devices mentioned above for pumping systems which, with PID control valve logic, control the process in which the input of valve data / position or other external signals is undesirable. The algorithm according to the present invention operates with flow reference data that may be mathematically determined depending on the various pump and motor parameters such as speed, torque or power, or on calibrated flow curves stored in the analyzer or on the external flow reference unit such as a flow meter.

Embodiments of the present invention may include one or more of the following features. Once the valve with PID control has reached its static normal state, a calculated flow value may be acquired and the current flow value obtained after the frequency (speed) of the frequency converter drive has dropped to be compared. In pressure control applications, the valve position can be optimized if the current flow is within 90-110% of the pump's optimum flow at current speed. A final check may be made on a wide open control valve by increasing the pump speed by a set amount and comparing the current flow value with a stored flow value; if the flow does not increase, the valve position is optimized. If the regulator already has its has reached the optimized state and either the actual engine torque increases by 5% or more, or the actual flow increases by more than 5% or more than the delay time, the valve optimization process can be restarted at maximum speed. Alternatively, if the regulator has already reached its optimized state and either the actual engine torque decreases by 5% or more, or the actual flow rate decreases by 5% or more, the valve optimization process may be restarted at the current operating point. A user-selectable, secondary test on a wide-open valve may be made whether a change in actual engine torque is 2% or more but less than 5% of the optimized state for the duration of the response delay; if this condition is true and the actual flow is greater than the optimized flow value after a one-step change in the speed, the optimization process can be restarted at maximum speed. In addition, the valve position may be optimized just before the speed threshold at which the flow condition of the algorithm is no longer true, or just before reaching the minimum speed if the flow condition is still true, alone or in conjunction with at least one of the aforementioned features.

BRIEF DESCRIPTION OF THE DRAWINGS

is a block diagram of a simple pump system according to the present invention

is a flowchart with the essential steps taken by an in shown regulator according to the present invention.

is a block diagram of in shown regulator with at least one module configured to perform the in shown essential steps.

FIG. 12 shows a flowchart for a process variable amount for constant flow control according to the present invention. FIG.

shows a flow chart for constant pressure control applications according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

shows the simple pump system according to the present invention generally with 2 is called and a controller 4 , a motor 6 and a pump 8th having. In operation and in accordance with the present invention, the controller determines 4 Flow reference data dependent on various pump and motor parameters, such as speed, torque, or power, or calibrated flow curves stored in an evaluation device (not shown) or an external flow reference unit, such as a flow meter (not shown), and uses the flow reference data to calculate the flow reference data pump 8th to regulate, as shown and described here.

shows an example of a flowchart, which is generally with 10 is called and the essential steps 10a and 10b of the algorithm for determining the pump flow through the regulator 4 can be realized according to the present invention. The determined flow value can also be used as input to a PID loop to control flow without an external flow meter or traditional gauges. The algorithm for determining the flow rate may be embedded in a frequency converter drive or in a programmable logic controller, as in FIG in terms of the regulator 4 shown.

Fig. 3: Controller 4

shows the main modules 4a . 4b and 4c of the regulator 4 , Many different types and types of regulators and control modules for controlling pumps are known in the art. One skilled in the art familiar with such controllers and control modules would be able to use control modules such as 4a and 4b implement and configure to perform functionality as described herein, that is, flow reference data as a function of various pump and motor parameters such as speed, torque, or power, or from calibrated flow curves stored in an evaluation device (not shown); or from an external flow reference unit such as a flow meter (not shown) and to use the flow reference data to the pump 8th like the in and as described above, according to the present invention. The evaluation device and / or the flow meter may be in at least one of the modules 4a and 4b or in a combination thereof or form part of it.

By way of example, the functionality of the modules 4a and 4b by hardware, software, firmware, or a combination thereof, but it is not intended to limit the scope of the invention to any particular embodiment thereof. In a typical software implementation, such a module would be one or more microprocessor-based architectures including a microprocessor, random access memory (RAM), read only memory (ROM), input / output devices and controller, and data and address buses to its connection. One skilled in the art would be able to program such a microprocessor-based implementation without undue experimentation to achieve the functionality described herein. It is not intended to limit the scope of the invention to restrict any particular implementation using a known or future developed technique.

The regulator 4 has further control modules 4c known in the art, which are not part of the underlying invention and which are not described in detail herein. For example, the other rule modules 4c have such an evaluation device and / or such a flowmeter. Incidentally, such evaluation devices for storing flow curves and / or the flow meters for providing the external reference data are known in the art and will not be described in detail here. In addition, it is not intended to limit the scope of the invention to any particular type or manner thereof which is either now known or will be developed in the future. Embodiments can be considered in which the evaluation device and / or the flow meter are also in at least one of the control modules 4a and 4b are included or form part of it.

engine 6 and pump 8th

engine 6 and pump 8th are known in the art and will not be described in detail here. In addition, it is not intended to limit the scope of the invention to any particular type or manner thereof which is either now known or will be developed in the future. Furthermore, the scope of the invention should also include the application of the method according to the present invention in relation to the regulation of the operation of a centrifugal pump, a centrifugal mixer, a radial fan or a centrifugal compressor.

realization

Today there are many processes with variable speed centrifugal pumps that work with control valves in combination with a PID controller. In this arrangement, a control valve is throttled to maintain the process setpoint using feedback signals from an external process transmitter and PID logic in a DCS (Distributed Control System), PLC Programmable Logic Controller) or other loop control device. In many cases the pump is over-sized and the cost of valve throttling can be high from an energy consumption point of view. In addition, when a variable speed pump is operated away from its optimum flow, the radial and axial loads acting on it increase. The increased loads may affect the service life of the bearings and seals and are likely to reduce the reliability of the system, which may lead to unplanned maintenance of the device. Costs associated with unplanned maintenance include equipment repair, production stoppages, and / or environmental remediation costs.

It is therefore advantageous to operate a system in which the pump speed can be lowered so that valve throttling is minimized and the pump can operate as close to its optimum flow rate as possible.

• – Maximale Pumpendrehzahl,
• – Minimale Pumpendrehzahl,
• – Motordrehmoment und
• – Motorleistung.

While many users want the benefits of lower operating costs and higher system reliability, they do not want to make changes to their control logic or provide external inputs. This invention solves this by using a variable speed drive (VFD) and control logic in an effort to optimize both the pump speed and the position of the control valve without requiring changes to the external control logic on the control valve. It also seeks to do this without the use of external inputs. The logic is as follows:
The VFD inputs to the logic include:

• - maximum pump speed,
• - minimum pump speed,
• - Motor torque and
• - engine power.

In one form, the logic operates with calculated flow data that can be mathematically determined from various pump and motor parameters such as speed, torque, or power, or from calibrated flow curves stored in an evaluation device. In practice, however, this logic could use any drive parameter that has a direct or semi-direct relationship to pump flow. In addition, while the functionality is without any external process signal in the foreground in this logic, but also a direct measurement of the flow (on a flow meter) is possible. The logic can be embedded in either a frequency converter drive (VFD) or a programmable logic controller (PLC).

shows a flow chart, generally with 50 for a process variable quantity for constant flow control, and applies to constant pressure control applications.

• Schritt 1 – Das Pumpensystem wird gestartet und fährt bis zur maximalen Drehzahl hoch. Eine Prüfung wird durchgeführt, um sicherzustellen, dass die Pumpe nicht mit Nulldurchfluss arbeitet – ein möglicherweise gefährlicher Zustand. Arbeitet sie mit Nulldurchfluss, so kann der Benutzer wählen, ob die Einheit gestört geschaltet (stillgesetzt) werden soll oder dem Bediener eine Warnung gesendet werden soll. Wenn der Durchfluss hergestellt ist, geht der Prozess, nachdem er eine Minute auf ein Ansprechen des Ventils mit PID-Regelung gewartet hat, zum nächsten Schritt über.
• Schritt 2 – Der Ventiloptimierungsprozess beginnt, sobald das Ventil mit PID-Regelung nach Ablauf der einminütigen Verzögerung den Sollwert bei der maximalen Pumpendrehzahleinstellung erreicht hat. Der aktuelle Durchflusswert wird als Q1 abgespeichert. Anschließend wird die Pumpe um einen benutzereinstellbaren Drehzahlschritt mit einer benutzereinstellbaren Rampensteigung allmählich verlangsamt. Sobald eine (benutzereinstellbare) Ansprechverzögerung abgelaufen ist, um dem Regelventil Zeit zum Wiederherstellen des Sollwerts zu geben, wird in einer Prüfung der aktuelle Durchfluss mit Q1 verglichen. Ist der Durchfluss unverändert (nur konstanter Durchfluss) oder hat er sich erhöht oder ist er gleich (nur konstanter Druck), so wird die Senkung der Drehzahl iterativ fortgesetzt, bis entweder die minimale Pumpendrehzahl erreicht ist oder der Durchfluss gesunken ist (nur konstanter Durchfluss). Ist der Durchfluss gesunken, so erhöht die Logik die Drehzahl leicht um einen halben Drehzahlschritt, bis der aktuelle Durchfluss größer oder gleich dem Durchfluss Q1 ist, bevor der Prozess zu Schritt 3 übergeht. Dies ist wichtig in Anwendungen mit hohen statischen Förderhöhen. Bei Druckregelungsanwendungen wird geprüft, ob der tatsächliche Durchfluss im Bereich von 90–110% des optimalen Durchflusses liegt, der Durchflusswert kleiner als Q1 ist oder die minimale Drehzahl erreicht ist, bevor der Prozess zu Schritt 3 übergeht.
• Schritt 3 – Der Zweck von Schritt 3 ist sicherzustellen, dass das Regelventil nicht weit geöffnet ist. Wird bei dieser Bedingung „grünes Licht” gegeben, so werden Pumpendrehzahl und Ventilstellung als optimiert betrachtet. Dauert eine Änderung des Motordrehmoments oder des Durchflusses >= +5% über die optimierten Werte länger als die Ansprechverzögerung, so wird daraus geschlossen, dass eine Erhöhung des Sollwerts eingetreten ist, und der Ventiloptimierungsprozess wird bei der maximalen Drehzahl neu gestartet. Beträgt die Änderung des Motordrehmoments oder des Durchflusses ≥ –5% des optimierten Drehmoments bzw. Durchflusses, so wird daraus geschlossen, dass der Sollwert gesenkt worden ist, und der Ventiloptimierungsprozess beginnt bei Schritt 2. Bei bestimmten Anwendungen kann ein Benutzer den Sollwert erhöhen, wenn das Regelventil bereits nahezu geöffnet ist. Dies darf nicht zu einer gleichzeitigen Änderung des Motordrehmoments von >= 5% führen. Für diese Bedingung ist ein benutzerwählbares Merkmal vorhanden, mit dem für einen Ventilzustand „weit geöffnet” geprüft wird, ob eine Änderung des Motordrehmoments >= +2% (aber weniger als 5%) vorliegt.

In the valve optimization process, there are three steps as follows:

• Step 1 - The pump system starts and ramps up to the maximum speed. A check is made to ensure that the pump is not operating at zero flow - a potentially dangerous condition. If it operates at zero flow, the user can choose to have the unit malfunctioned (shut down) or to send a warning to the operator. When flow is established, after waiting one minute for the valve to respond to PID control, the process moves to the next step.
• Step 2 - The valve optimization process begins as soon as the valve with PID control reaches the setpoint at the maximum pump speed setting after the one-minute delay has elapsed. The current flow value is stored as Q1. Subsequently, the pump is gradually slowed down by a user adjustable speed step with a user adjustable ramp pitch. Once a (user settable) response delay has elapsed to allow the control valve time to recover the setpoint, a test compares the current flow with Q1. If the flow is unchanged (constant flow only) or has increased or is the same (constant pressure only), then the reduction in the speed is continued iteratively until either the minimum pump speed has been reached or the flow has dropped (only constant flow) , If the flow has dropped, the logic slightly increases the speed by half a speed step until the current flow is greater than or equal to the flow Q1 before proceeding to step 3. This is important in applications with high static heads. For pressure control applications, it is checked if the actual flow is in the range of 90-110% of the optimum flow, the flow value is less than Q1, or the minimum speed is reached before the process goes to step 3.
• Step 3 - The purpose of step 3 is to ensure that the control valve is not wide open. If "green light" is given in this condition, the pump speed and valve position are considered optimized. If a change in engine torque or flow> = + 5% over the optimized values lasts longer than the response delay, it is concluded that an increase in the target value has occurred and the valve optimization process is restarted at the maximum rotational speed. If the change in engine torque or flow is ≥ -5% of the optimized torque or flow, it is concluded that the setpoint has been decreased and the valve optimization process begins at step 2. In certain applications, a user may increase the setpoint if the control valve is already almost open. This must not lead to a simultaneous change of the motor torque of> = 5%. For this condition, a user-selectable feature is provided to check for a "wide open" valve condition whether there is a change in engine torque> = + 2% (but less than 5%).

It should be noted that although the calculated flow values have been used in the logic presented here, values of torque or power could be substituted for the flow. The logic constantly checks for the calculated flow value for dry run, minimum flow (flow too low), or run out conditions (flow too high) and then either warns the user or shuts down the unit and malfunctions or automatically resets the fault and restarts the unit (if so configured) about the pump protection logic shown in provisional patent application Serial No. 60 / 780,529 (05GI002 / 911-2.22-1), filed on Mar. 8, 2006, and the corresponding regular patent application, Serial No. 11 / 601,373 (05GI002 / 911-2.22-2), filed Nov. 17, 2006, both of which are incorporated by reference in their entirety.

OTHER APPLICATIONS

Existing systems that operate with a control valve logic in which the setpoint is achieved by valve throttling, usually at a fixed engine speed. This logic, embedded in a VFD or PLC, would allow optimization of pump speed and control valve position to reduce operating costs and increase system reliability.

Scope of the invention

It should be understood that unless otherwise stated herein, any of the features, characteristics, alternatives, or modifications described with respect to a particular embodiment set forth herein are also applied to any other embodiment described herein or can be included therein. In addition, the drawings in this document are not to scale.

Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing or various other additions and omissions may be made thereto without departing from the spirit and scope of the present invention.

Claims (18)

A regulator, comprising: At least one module configured to determine flow reference data in response to various pump and motor parameters, such as speed, torque or power, or from calibrated flow curves stored in an analyzer or from an external flow reference unit, such as a flowmeter, and at least a module configured to use the flow reference data to control a frequency converter drive driven centrifugal pump, radial blower, impeller, or centrifugal compressor in a PID control valve system where once a valve of the PID controlled valve system is in its static normal condition has detected a calculated flow value and compared with the current flow value obtained after the frequency (speed) of the frequency converter drive has dropped. A regulator according to claim 1, wherein the valve position is optimized shortly before the speed threshold at which the flow condition of the algorithm is no longer true. Regulator according to claim 1, wherein the valve position is optimized shortly before reaching the minimum speed, if the flow condition is still true. A regulator according to claim 1, wherein in pressure control applications the valve position is optimized if the current flow is within 90-110% of the optimum flow rate of the pump at the current speed. A regulator according to claim 1, wherein a final check is made on a wide open control valve by increasing the pump speed by a set amount and comparing the current flow value with a stored flow value; if the flow does not increase, the valve position is optimized. A regulator according to claim 1, wherein in the case that the regulator has already reached its optimized state and either the actual engine torque increases by 5% or more or the actual flow exceeds the delay time by 5% or more, the valve optimization process becomes maximum Speed is restarted. A regulator according to claim 1, wherein in the event that the regulator has already reached its optimized state and either the actual engine torque decreases by 5% or more or the actual flow rate decreases by 5% or more, the valve optimization process restarts at the current operating point. A regulator according to claim 1, wherein a user-selectable secondary test is performed on a wide-open valve, whether a change in the actual engine torque is 2% or more but less than 5% of the optimized state for the duration of the response delay; if this condition is true and the actual flow is greater than the optimized flow value after a one-step change in speed, the optimization process is restarted at maximum speed. A method comprising the steps of: - Determination of flow reference data depending on various pump and motor parameters such as speed, torque or power or on calibrated flow curves stored in an evaluation device or from an external flow reference unit such as a flow meter, and - Use the flow reference data to control a frequency converter drive driven centrifugal pump, radial blower, impeller or centrifugal compressor in a PID control valve system, once a valve of the PID control valve system has reached its static normal state, a calculated flow value and compared with the current flow value obtained after the frequency (speed) of the frequency converter drive has dropped. The method of claim 9, wherein the valve position is optimized shortly before the speed threshold at which the flow condition of the algorithm is no longer true. The method of claim 9, wherein the valve position is optimized shortly before reaching the minimum speed, if the flow condition is still true. The method of claim 9, wherein in pressure control applications, the valve position is optimized if the current flow is within 90-110% of the optimum flow rate of the pump at the current speed. The method of claim 9, wherein a final check is made on a wide open control valve by increasing the pump speed by a set amount and comparing the current flow value with a stored flow value; if the flow does not increase, the valve position is optimized. Method according to Claim 9, in which, in the event that the controller has already reached its optimized state and either the actual engine torque increases by 5% or more, or Actual flow longer than the delay time by 5% or more increases, the valve optimization process is restarted at maximum speed. Method according to claim 9, wherein in case the regulator has already reached its optimized state and either the actual engine torque decreases by 5% or more or the actual flow rate decreases by 5% or more, the valve optimization process restarts at the current operating point. The method of claim 9, wherein a user-selectable secondary test is performed on a wide open valve, whether a change in actual engine torque is 2% or more but less than 5% of the optimized state for the duration of the response delay; if this condition is true and the actual flow is greater than the optimized flow value after a one-step change in speed, the optimization process is restarted at maximum speed. A regulator, comprising: At least one module configured to determine flow reference data in response to various pump and motor parameters, such as speed, torque or power, or from calibrated flow curves stored in an analyzer or without a flowmeter, and - at least one module configured to use the flow reference data to control a frequency converter driven centrifugal pump, a radial fan, a centrifugal mixer or a centrifugal compressor in a PID control valve system, once a valve system valve with PID control static state, a calculated flow value is detected and compared with the current flow value obtained after the frequency (speed) of the frequency converter drive has dropped. A method comprising the steps of: - Determination of flow reference data in relation to various pump and motor parameters such as speed, torque or power or from calibrated flow curves stored in an analyzer or without a flowmeter, and - Use the flow reference data to control a frequency converter drive driven centrifugal pump, radial blower, impeller or centrifugal compressor in a PID control valve system, once a valve of the PID control valve system has reached its static normal state, a calculated flow value and compared with the current flow value obtained after the frequency (speed) of the frequency converter drive has dropped.

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